Only a few years ago advocates of marriage equality were wary of pursuing their cause in the federal courts because they feared that the U.S. Supreme Court might deal a fatal blow to their hopes.

But events have moved quickly on gay marriage, and public opinion has shifted dramatically. This week the Supreme Court is hearing arguments in two cases challenging laws limiting marriage equality for gays and lesbians.

It is far from clear that the court will side with advocates of gay marriage, but the transformation of public attitudes has become a victory in itself for those promoting equality and respect. The court may well remain hedged in by old ideas, standing by laws, now under challenge, that codify old biases. But time is on the side of those who favor equality, and unfavorable rulings this year may one day seem like footnotes marking the demise of an era of intolerance.

Can constitutional principles become old and outdated, or does fealty to the law require our justices to uphold unchanging interpretations despite shifts in public opinion? Conservatives such as Justice Antonin Scalia believe the original intention of the Founders should govern the court’s interpretation of cases today and that public opinion is an unreliable weather vane.

But history has shown us that past interpretations of the law have sometimes been governed by biases long since abandoned in society. If the court is willing to examine the assumptions upon which past cases were based, it may conclude that new interpretations of the law are actually truer to the principles of the Constitution.

That is the process that allowed the court’s rulings on race to grow over time. At one time the court ruled that slaves were property with no rights whatsoever. After slavery was abolished, the court ruled that racial segregation was nevertheless permissible. Sixty years later the court found that racial segregation of schools was, after all, contrary to the Constitution. And about a decade later it ruled that state laws barring interracial marriage were unconstitutional.

History is not frozen. Our understanding of history grows over time, and so should our understanding of the principles of the Constitution. Nine states and the District of Columbia have decided that constitutional guarantees of equal treatment under the law mean that people cannot be barred from choosing a marriage partner of the same sex.

It has been a long road. In his Inaugural Address this year, President Obama mentioned Stonewall in the same breath as he mentioned Seneca Falls and Selma. Stonewall was the Greenwich Village bar where police persecution ignited protests that became the catalyst for the burgeoning gay rights movement. That was 1969.

The AIDS epidemic of the 1980s highlighted two contrary trends: public indifference to the suffering of gay people and public recognition of the humanity of gay people. Over time, the willingness of gay people to step forward and speak up for themselves taught society at large the lesson that homosexuals are not a people apart. They number among our leaders and among our relatives, neighbors and friends.

This week the U.S. Supreme Court is considering two cases. One challenges a lower court ruling that rejected Proposition 8 in California, the voter-passed law that bars gay marriage. The other challenges the federal Defense of Marriage Act, which denies federal benefits to same-sex couples and allows states to refuse to recognize same-sex marriages from other states.

Chief Justice John Roberts was apparently concerned that authorizing same-sex marriage would alter the definition of marriage. Many opponents of gay marriage cling to the notion that traditional definitions exist as holy writ rather than as a legal construct, fabricated in history out of outdated biases and religious presumptions.

Vermont has traveled the long road to gay marriage, contending with the violence and bigotry that have hounded gay people over the generations, struggling over basic questions of equal rights, moving toward a more inclusive understanding of what love and marriage mean. It has been an inspiring journey. It is inspiring that the nation is now headed in that direction.